A fuel cell is a power source that outputs electric energy directly converted from chemical energy of the fuel, therefore its energy conversion efficiency is high, and consequently it is an environment-friendly power source. Among fuel cells, a fuel cell of the type using hydrogen and oxygen as the fuels is becoming practical use as a pollution-free power source mainly for automobiles, because their reaction product is water.
Now, in the automobiles having such a fuel cell as their power source, there are systems, one of which carries a cylinder filled with a high pressure hydrogen gas and uses hydrogen gas thereof as a fuel, and the other of which carries a fuel such as petroleum or methanol and uses the hydrogen produced by a hydrogen producing apparatus so called fuel reformer from fuel thereof.
Since hydrogen gas has an extremely large risk of explosion by mixing with air, it is more desirable for safety to use the system which carries a fuel such as petroleum or methanol and produce only a necessary amount of hydrogen gas from fuel thereof when needed, than to use the system which carries a cylinder filled with a high pressure hydrogen gas and use hydrogen gas thereof.
However, since a conventional hydrogen producing apparatus is large in size and consumes a large amount of energy for hydrogen producing, there has not been the practical use for automobiles or the like. Mention thereof may be made more specifically by referencing to an exemplary hydrogen producing apparatus in the prior art.
In this connection, though apparatuses for producing hydrogen gas from methanol have not existed, the art is known for generating hydrogen by gaseous methanol decomposition (Japan Patent laid open H9-187653 [1997], Yoshikazu Usami, et al., ‘Catalytic methanol decomposition at low temperature over palladium supported on metal oxides’ Applied Catalysis A: General 171 [1998] 123-130, Kiyoharu NAKAGAWA, et. Al., Diamond-supported metal catalyst: a novel medium for hydrogen production from methanol decomposition, Catalysis Letters, 2002, vol.80, No.3, 4, p. 161-164), and the explanation of the conventional apparatus described below is based on this art.
FIG. 5 is a diagrammatic view of a conventional hydrogen producing apparatus for producing hydrogen gas from methanol. In the Figure, liquid methanol 51 is introduced into a methanol vaporizer 53 heated to a temperature of about 300° C. by a heater 52 such as a burner to be vaporized into methanol gas 54, and the methanol gas 54 is introduced into a catalyst bed 55. As catalyst bed 55 has a layer structure of catalyst 56 comprising catalyst particles 56 of Pd/CeO2 or the like which can decompose methanol into hydrogen gas and other gaseous components mainly including carbon dioxide gases, the vaporized methanol 54 introduced into the catalyst bed 54 is decomposed by the catalyst 56 into hydrogen and other gases mainly including carbon dioxide 57. The catalyst bed 55 needs to be heated for activating the catalyst 56 to a temperature of about 300° C. by a heater 52 such as a burner. Hydrogen and other gases mainly including carbon dioxide 57, which are produced through the decomposition by the catalyst bed 55, are introduced into a separator 58 where they are separated into hydrogen gas 60 and other gases 59 whereby hydrogen gas 60 is produced. The separator 58 may, for example, be a selective adsorber adapted to selectively adsorb carbon dioxide gas.
In the vaporizer 53 of the apparatus, however, it is necessary to maintain the vaporizer 53 as a whole at the high temperature of about 300° C. by heating for maintaining the vaporizing rate always high, by which producing immediately when needed, an amount of hydrogen gas needed for generating a driving force of the automobile, and it has the size which can not be ignored as compared with the size of automobile.
Also, in the catalyst bed 55 of the apparatus, however, it is necessary to maintain the catalyst bed 55 as a whole at the high temperature of about 300° C. by heating for maintaining the reaction rate of the catalyst always high, by which producing immediately when needed, an amount of hydrogen gas needed for generating a driving force of the automobile, and it has the size which can not be ignored as compared with the size of automobile.
Thus, the conventional hydrogen producing apparatus is too large in size and in weight, and consumes too much energy for heating the vaporizer and the catalyst bed, to be equipped in practice for any automobile.